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How can I know which Internet proxies servers are available in a LAN? The computer I'm using is running Windows.

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3 Answers 3

In general, a scan of port 53 (tcp should be okay), for the entire LAN would show you which computers are running the DNS service. You can get nmap for Windows to do this.

If you suspect a computer might be a DNS server, you can telnet <ip> 53 and see if the sessions starts. You could of course also use nslookup.

Edit:
So you want to scan for tcp ports 80,8080,8081, using nmap you could nmap -sT -pT:80,8080,8081 192.168.1.1/24 to scan the 192.168.1.1 255.255.255.0 network, and look for 'open' ports.

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Okay, never mind, I read that at as DNS, I don't know why... –  Kyle Brandt Dec 10 '09 at 13:17
    
Sorry. I originally asked for DNS server but what I really wanted to ask for are Internet proxies to configure my web browser. –  Anonymous Dec 10 '09 at 13:18
    
Ah, good, I'm not totally crazy :-) –  Kyle Brandt Dec 10 '09 at 13:19
    
So yes, you could use nmap to scan for those common ports Massimo mentioned and then see if they are a proxy. –  Kyle Brandt Dec 10 '09 at 13:20

You can't.

A proxy server could be listening on any TCP port, and although 80, 8080, 8081 and similar ones are quite common, there's no guarantee that if one of such ports is open on a given host, that is actually a proxy server.

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I know 2 proxies in this LAN listening at 8080. How can I know all the servers listening at 8080? –  Anonymous Dec 10 '09 at 13:19
    
Use a port scanner, such as NMAP. But beware, this could make your network admin quite unhappy. –  Massimo Dec 10 '09 at 13:21
    
Use nmap, as I mentioned in my post. –  Kyle Brandt Dec 10 '09 at 13:21

seems like a pretty simple question.

there are a number of windows clients that look like they will find proxies

try

http://www.google.com/search?q=windows+proxy+scanner

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